Thermosetting foams have been produced by the reaction of polyester resins with methylene diisocyanate. Such foams have been characterized by high compressive, tensile and flexure strengths. However, the high viscosity of the polyester resin in the reaction mixture tends to make the processing and preparing of the foams, on a commercial and continuous basis, difficult. In such rigid polyester foams, the K-factors are often quite high; that is, the foams are of poor insulation quality, due to the incompatibility of the fluorocarbon blowing agents in the reaction mixture. The polyester foams, of both a rigid and a flexible nature, tend to burn, because they are oxygen-rich; however, such foams produce low smoke values.
Polyisocyanates have been reacted in the presence of a trimerization catalyst, to produce polyisocyanurate foams, in an attempt to produce foams which produce high char resistance to fire and low smoke values. However, in such foams, only high char resistance has been obtained. The rigid trimerized polyisocyanurate-type foams produced tend to have higher K-factors than urethane foams, but also are quite brittle and frangible in nature. The trimerization of methylene diisocyanate produces a foam of low smoke value, but black in color, and which is relatively nonburning. The problems with such methylene diisocyanate trimerized foam are the poor compressive strength and high friability. In order to correct or to mask these undesirable properties, it has been the practice to incorporate small amounts of urethane polyols, such as sucrose amine, glycols or aromatic amines, in the isocyanate reaction mixture, to produce a modified, urethane-polyisocyanurate foam. However, the addition to such urethane polymers leads to degradation in the fire and smoke properties of the modified foam.
Polyurethane foams; that is, foams prepared by the reaction of a polyhydroxyl compound and a polyisocyanate in the presence of a urethane catalyst, provide foams of unacceptable flame resistance. It has been proposed that such polyurethane foams be modified by the addition of a nonreactive amount of a melamine powder in the reaction mixture, to confer enhanced flame resistance on the resulting polyurethane foam (see U.S. Pat. No. 4,221,875, issued Sept. 9, 1980).
It is desirable to prepare an inexpensive polyester thermosetting foam composition which avoids the disadvantages of the prior-art polyester foams, the rigid polyisocyanurate foams, the modified polyurethane foams and the polyurethane foams of the prior art.